Container inspection apparatus with plural detectors and rotating projection system

ABSTRACT

An apparatus for inspecting containers is disclosed in which a rotating and nutating projection of an inspection field is sensed by a photocell arrangement, each cell being provided with one or several light stops. The output signals of adjacent cells are a-c processed in different channels.

I United States Patent [191 [111 3,708,680

Calhoun 1 Jan. 2, 1973 54 CONTAINER INSPECTION 3,133,640 5/1964 Calhounet al. ..250/223 B ux APPARATUS WITH PLURAL 3,292,785 12/1966 Calhoun..250/223 B DETECTORS AND ROTATING PROJECTION SYSTEM FOREIGN PATENTS ORAPPLICATIONS Inventor: Fredrick L. Calhoun Torrance 702,548 1/1965Canada ..250/223 B Cahf' Primary Examiner-James W. Lawrence [73]Assignee: Automatic Sprinkler Corporation of Assistant Examiner-D. C.Nelms America, Cleveland, Ohio Att0rneySmyth, Roston and Pavitt [22]Filed: June 4, 1968 [57] ABSTRACT [21] Appl' 734394 An apparatus forinspecting containers is disclosed in which a rotating and nutatingprojection of an inspec- [52] US. Cl. ..250/223 B, 356/240 tion field issensed by a photocell arrangement, each [51] Int. Cl. ..II0lj 39/12 cellbeing provided with one or several light stops. The [58] Field Of Search.250/ 40 output signals of adjacent cells are a-c processed in differentchannels. [56] References Cited 12 Claims, 6 Drawing Figures UNITEDSTATES PATENTS 3,081,666 3/1963 Calhoun et al. ..250/223 B X' far e 6/70PATENTEDJAN 2 ms 3.708.680

CONTAINER INSPECTION APPARATUS WITI-I PLURAL DETECTORS AND ROTATINGPROJECTION SYSTEM The present invention relates to an apparatus forinspecting containers, such as bottles for cleanliness.

When bottles or other, preferably transparent devices, arephotoelectrically scanned, small particles of foreign matter aregenerally difficult to detect. Systems are known employing a rotatingreticle as part of a photoelectric scanning system to facilitatedetection of small foreign particles. The reticle intercepts the lightfrom the illuminated bottle to a photocell which also forms part of thephotoelectric scanning means.

The reticle is made up of alternating opaque and transparent areas whichare successively interposed between any foreign particles in the bottleand the photocell. The optical input of the photocell thus varies andthe resulting electrical output signal includes an alternating componentwhich has a frequency related to the alternating speed of the reticleand the number of alternating opaque and transparent areas of thereticle. If foreign particles are not present in the bottle, thephotocell receives light at a constant level, and its output issubstantially a direct current and unaffected by the rotation of thereticle accordingly.

A system of this type works generally satisfactorily, except thatcentrally located foreign particles to be detected can escape detection.A small centrally located particle, scanned through alternating opaqueand transparent reticle. portions of comparable or even smallerdimensions in angular direction, will produce little modulation of thelight. To overcome this problem of a low system sensitivity in thecenter of the inspection field, it has been suggested to differentiatebetween the total field of inspection and the instantaneous field ofinspection, the latter being smaller than the former and beingeccentrically located thereto. The instantaneous field of inspection isprimarily determined as to its overall dimensions of the optical inputaperture of the photoelectric device. The opaque portions of the reticleoperate as temporary light stop, blocking light from a portion of theinstantaneous field of inspection as usual. The scanning and inspectiondevices are constructed so that the instantaneous field of inspectionsweeps over the total field of inspection, whilethe light stop (reticle)positions vary in relation to the instantaneous field of inspection.

If the diameter of the instantaneous field of inspection is, forexample, only a little larger than the diameter of the total field ofinspection, one obtains an almost uniform sensitivity for the entire(total) inspection field. The presence of foreign particles exhibitsitself as signals of particular frequency in the output of thephotocell. An analysis shows that the particular frequency is within aband defined by the characteristics of the reticle, as mentioned above,by the rotational speed thereof, as well as by the sweeping speed of thescanner. This has the advantage that foreign particles representingsignals can still occur only within a narrowly selectible frequencyband, and through appropriate tuning techniques in the output circuit ofthe photocell, the signal-to-noise ratio of the system is basicallyhigh. .Thus, the response threshold representing minimum size of aparticle recognized as the foreign particle, can be rather low. Thatminimum particle size is a substantially uniform one for the entiresurface to be inspected.

Systems of this type operate very satisfactorily but the followingproblems have arisen. It may happen that a relatively large foreignparticle or dirt patch is located so that it is partially covered byoperation of one or more opaque portions of the reticle and partiallyuncovered by one or more transparent portions of the reticle; as thereticle rotates, the overall light balance reaching the photocell is notor very little changed, i.e., the modulation is self-canceling.

A related self-canceling situation arises as follows: Since thecontainers to be inspected are in motion during the inspection, thelooking time or inspection period is rather short. In particular, onesweep of the instantaneous field of inspection over the total inspectionfield should suffice. It may now occur that two particles are locatedclose to the periphery of the total inspection field and such thatcovering and uncovering by opaque reticle portions alternate; again thelight reaching the photocell is modulated very little. Thisself-canceling could be avoided by several sweeps over the totalinspection field with a nonintegral relation between sweep rate andreticle rotation. However, an extended looking time or inspection periodoperates ultimately as a slow down of container transport speed which isundesirable.

Another problem is the following. The inspection system has basicallythree important optical planes. One plane is the bottom of the containerto be inspected, which, so to speak, is the optical object plane. Then,there is the plane of the photocell or photodetector onto which an imageof the bottom of the container is either projected directly or thephotodetector is positioned so that it can observe (virtually) an imageproduced from the bottom. In addition, there is the reticle. In view ofthe fact that the reticle is mounted for rotation, it cannot bepositioned in either plane. On the other hand, the reticle must bepositioned such that the opaque portions when projected into theinstantaneous field of inspection have rather sharp boundarres.

It has to be observed now that an inspection station is used to inspectdifferent bottles at different times. Since the inspection stationshould be as close as possible, to the surface to be inspected, (such asthe container bottom), the distance of the station from that surfacewill vary with the height of the bottle. In other words, the inspectionstation must be constructed for variable optical conditions. In view ofthe three planes involved, such adaption invokes considerabledifficulties. Of course, that problem could be solved by having acompletely new optical system for each separate bottle to be inspected.However, the invention, while solving the self-canceling problemsoutlined above, points also to a solution which makes the adaption ofthe system for different bottles considerably easier.

In essence, the inspection system, in accordance with the preferredembodiment of the invention, includes an optical imaging or projectionsystem which provides a rotating instantaneous inspection field andwhich, in addition, is caused to nutate over the total field ofinspection. A stationary reticle is preferably provided directly in theplane of the photo detector which is comprised of a plurality of cells,each being partially covered by one or more opaque spokes of thereticle. The provision of several photocells results in an electricallyproduced coarse modulation of the outputs of each photocell when theprojected inspection field sweeps over the detectors. The provision of afew opaque reticle spokes above each cell produces optically a finemodulation effective as such in the output signal of each photocell.

Electric circuit means are connected to the several photoelectric cellssuch that the output signals of adjacent cells are processed separately,particularly as to any a-c components of their output signals in thefrequency band of interest. As the instantaneous field of inspectionperforms a double sweep, while the reticle-photocell structure remainsstationary, the cancel ing effect outlined above will not occur. If theprojection of a large dirt patch sweeps over the cells, the output ofany cell will not be influenced by the fact that the projection of thesame dirt patch sweeps also over a neighboring cell but at differentphase. Independent processing of the signals of adjacently located cellsprevents cancelation of signals which are possibly in phase oppositionas to the,'patch sweepover them.

Since photocells and reticle form a nonrotatable, uniform structure forpositioning in the same plane, such structure could be madelongitudinally adjustable along the optical axis as a means for adaptingthe unit to differently high bottles, i.e., to a different objectdistance.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention, the objects and featuresof the invention and further objects, features, and advantages thereofwill be better understood from the following description taken inconnection with the accompanying drawing in which:

FIG. 1 illustrates a container inspection and reject control system inwhich the invention can be practiced with advantage;

FIG. 2 illustrates schematically in perspective view the optical systemwithin the apparatus in accordance with the preferred embodiment of theinvention and includes a circuit block diagram for processing photodetector signals;

FIG. 3 illustrates a section view into a portion of the inspectionstation illustrated in FIG. 1;

FIG. 4 illustrates a plan view of the photo detectorreticle system inthe station as illustrated in FIG. 3; and

FIGS. 5 and 6 are waveforms of photo detector output signals as they canoccur during operation of the system shown in FIGS. 1 through 4.

Proceeding now to a detailed description of the drawings, in FIG. 1thereof, there is illustrated somewhat schematically the layout of acontainer inspection and reject station in which the preferredembodiment of the present invention is practiced with advantage.Containers 10, such as bottles, are transported on a conveyor belt 11,past an inspection station 12. The container 10 is presumed to betransparent to some extent, i.e., its wall, and most particularly itsbottom, is not completely opaque. Within this rule, however, the rangeof permissible transparency may vary widely. For example, the bottle 10may be a clear glass bottle but it can also be a dark brown or greenbottle, such as commonly used for bottled beer or other beverages.

The specific construction of the conveyor belt 11 and of its drivemechanism, is not important. However, the conveyor belt 11 must beprovided with windows 13 or other types of transparent sectionspermitting passage of light from a stationary light source 14 positionedunderneath conveyor belt 11. The light source 14 thus illuminates abottle 10 when on such a window 13 from below. In particular, the bottomof a bottle is illuminated when passing through the range of lamp 14 andwindow 13. The bottom of the bottle itself modulates the illumination,but only as a more or less uniform attenuation; foreign particlesoperate as partial or complete, contrast-producing light stops andlocally diminish the light passing through accordingly.

The lamp 14 is positioned essentially in optical alignment with anoptical system in that portion of the inspection station 12, which isdisposed above the conveyor l1 and described in greater detail later inthis specification. The inspection station 12 includesoptical-electrical conversion means which provide signals representativeof cleanliness of a bottle when passing through the range of theinspection station 12. As during different inspection runs differentgroups of different height containers may pass the inspection station,the station may be positioned adjustable as to its distance from belt11, and as indicated by the double arrow.

Farther down the path of the conveyor 11 a reject device 15 is providedwhich can remove bottles from the conveyor 11. Devices of this type are,for example, described in my US. Pat. No. 3,279,881. The reject device15 is under control of the reject control circuit 16 receiving thesignals from the inspection station 12 representing the presence orabsence of foreign particles in a container 10 that is being inspected.In case a foreign particle has been detected, the output of station 12triggers reject control 16 to cause the reject device 15 to remove thebottle from the conveyor 11, for example, by passing it to a branchingconveyor or the like. A clean container causes the reject control andthe device 15 to remain disabled. The reject control may include signalstorage facilities for reject signals in order to bridge the travel timeof a container from station 12 to the actuating range of reject device15.

After describing the general layout of the system in which the inventionis practiced, I proceed to the description of FIGS. 2 and 3, whichillustrate in greater detail the salient components of inspectionstation 12. The inspection station 12 includes a housing 20 of which isshown only the lower or bottom portion. In the interior of housing 20there is a frame 22 for mounting the several elements described in thefollowing. The bottom of housing 20 has an aperture 21 which isoptically aligned with the lamp l4, i.e., it is optically aligned withthe desired position for a container when being inspected. The specificalignment of a container with aperture 21 can be monitored by separatedetectors (not shown) which enable the inspection station for limitingthe looking time or inspection period to a period beginning shortlybefore and ending shortly after alignment of a container 10 with theaperture 21.

A first optical unit 25 having optical axis 25 is provided in aperture21 and is comprised of a primary lens 26 and of a wedge prism 27. Thewedge prism 27 causes a relative deflection of an optical path alongaxis to run along an axis 27. The two elements 26 and 27 are mounted inthe interior of a hollow pulley 28 which is journaled by bearings 24, sothat the axis of rotation coincides with the optical axis 25' of theprimary lens 26 and traverses the center of aperture 21. The pulley 28is driven through a belt 29 coupled to a drive 30 illustrated onlyschematically.

A second pulley 31 is joumaled above pulley 28 and coaxially thereto.Pulley 31 is likewise hollow and a dove prism is mounted in the hollowspace. Dove prism 35 is in the optical path along axis 25. Pulley 31 isparticularly journaled by means of bearings 32 in support frame 22 andis driven through a belt 33 by means of a drive 34. The two drives 30and 34 are illustrated only schematically. Basically they may have thesame prime mover, such as a motor, and different gears or othertransmission means provide separately motive power to the two belts 29and 33. For reasons below the two pulleys 31 and 28 have differingspeeds.

A turret is provided with two disks 41 and 42, mounted one above theother on a shaft 43, and both above the arrangement in housing 20, asdescribed thus far. Shaft 43 is disposed for rotation in frictionbearings 48 and 49, mounted at frame 22. Disk 41 has several aperturesin which are received thimbles, such as thimble 44, each thimble havinga secondary object lens, such as 45. The several thimbles in turret disk41 are selectively positionable into optical axis 25' so that therespective secondary lensed form different projection systems togetherwith primary lens 26. The secondary lens in thimble 44 is illustrated inoptically aligned position with the elements 26, 27 and 35, accordingly.Secondary leans 45 together with primary lens 27 thus constitutes aparticular optical projection system for imaging an object (namely, thebottom of a particular type container) into an image plane in which ismounted a photoelectric detector system 50.

The photocell means 50, particularly its effective optical plane, couldbe mounted for vertical displacement along axis 25. The initialselection of thimbles as holders for the different secondary lensespermits placement of any of the secondary lenses in different horizontalplanes along axis 25' (see thimble 44a). An exchange of the secondarylenses may become necessary in order to adapt the system more generallyto different objects looked at through the system as described. Forexample, the bottom of differently high containers will have differentdistances from the inspection station. As was mentioned above, thehousing 20 should be adjustable in relation to the belt 11 forinspection of different height containers so that the aperture 21 can bepositioned always rather close to the top of the containers. This, ofcourse, changes the distance between the primary (and secondary) lensand the bottom of a container to be inspected, while the distancebetween the primary lens and theimage plane (plane of the detectorremains constant. In order to adapt the system optically to thisvariation in object distances (optically speaking), the secondary lensesare being changed through the turret, for placing the thimble with themost suitable secondary lens among those provided in the turrett intothe optical path along axis 25'.

It is commonly believed that a dove prism should be traversed byparallel wavefronts, otherwise distortions result. However, it was foundthat if the focal length of the primary lens is selected to be abouthalf way in the range of object distances from container bottomsexpected to occur, which range may cover object distances at about a 2:1ratio, then the resulting optical distortion has no effect on theoperation of the apparatus.

The second disk 42 of turret 40 on shaft 43 is provided with another setof thimbles including illustrated thimble 46. The thimble 46 defines aparticular field stop-aperture 47 in the optical imaging path along axis25' and positions such aperture in front of photo detector system 50.The photo detector system 50 is, for example, comprised of fourpie-shaped or sector-shaped solar cells 51, 52, 53 and 54 with a sectorangle of 90 with reference to the center (see FIG. 4). Each of thesesolar cells of the photo detector systems is provided with an overlaidmask but that mask can be common to the four photocells. That mask hasalternating opaque and transparent sector-shaped areas respectivelydenoted 61 and 62. Each photocell has three sectorshaped or pie-shaped,exposed portions which can receive light, while two pie-shaped sectorsare blocked off. The three sector windows 62 for any one of thephotocells each has an angle with reference to the common center of thesystem by 18, and the opaque reticle spokes 61 have, likewise, a sectorangle of 18.

The optical system as described can be understood best from FIG. 2. Thefield 10a represents the bottom of a container to be inspected; moregenerally it is the total inspection field. The optical axis 25' runsthrough the center of that inspection field at about the middle of theinspection period. However, it is presumed that the field 10a moves verylittle in relation to that axis during the contemplated short inspectionperiod as indicated by dotted lines representing maximum displacement ofthe total inspection field from the position in the middle of theinspection period. The field stop 45 when (hypothetically) projectedonto field 10a through the optical system 26-45 outlines theinstantaneous inspection field 45' which, by operation of the wedgeprism 27, is eccentric within the inspection field 10a. The wedge prism27 thus causes the instantaneous inspection field, particularly thecenter thereof, to be deflected. This can be restated as follows: thewedge prism 27 causes the center'of field 45', as projected along axis27', to be deflected for projection into and along axis 25'. As wedgeprism 27 rotates, because pulley 28 is being rotated by drive 30, theinstantaneous inspection field 45 nutates around the axis 25 to sweepthe entire inspection field 10a.

The optical system as comprised of primary lens 26, secondary lens 45and aperture stop 47 images the portion 45' of inspection field 10a ontophotocells 50. The image of field 45' is seen by the photocell mosaic 50through the several windows 62 of the reticle only. The spokes 61' asprojected by the optical system into the instantaneous field at anyinstant define therein blind areas or areas of temporary noninspection61'. These areas 61' are interspaced in the (hypothetical) projection62' of the three windows 62 of each photocell. These hypotheticallyprojected windows outlining the areas 62 are the individualinstantaneous inspection fields. Together they define the commoninstantaneous inspection fields.

For the moment it shall be assumed that wedge prism 27 does not rotate,so that the field 45' is stationary relative to and within field 1011.As dove prism 35 rotates due to rotation of pulley 31 by operation ofdrive 34, the projected reticle field rotates about the instantaneouscenter defined by the intersection of axis 27' and the plane of theobject field, which is the bottom of the bottle to be inspected. Thus,the instantaneous inspection field is fully inspected, particularlyafter rotation of dove prism 27 through an angle equal to the half thesector angle of the opaque spokes. As the sector angle was presumed to18, full inspection has occurred after a rotation of dove prism by 9. Itwill be recalled that an image projected through a rotating dove prismrotates at twice the speed of the dove prism. As the dove prism rotatesat a higher speed than wedge prism, field 45' has moved very littleduring the 9 deflection of dove prism.

Each photocell, such as S0, 51, etc., defines a quarter pie-shapedinspection field at any instant, composed of three portionscorresponding to the three windows 62, resulting from thesuperimposition of opaque spokes as provided by the reticle. As aconsequence, a twofold light modulation is produced by operation ofrotation of the instantaneous field of inspection through the doveprism. A fine modulation results from the sweep of the field asprojected onto cells 50 over the reticle spoke-window sequence of eachand all photocells. A coarse modulation results from the sweep of thatprojected field over the individual photocells as a whole. The finemodulation will result specifically from small particles, the coarsemodulation from larger ones. Since additionally small particles aredetected to some extent through the coarse modulation as defined whilelarge particles and extensive patches will, to some extent, produce finemodulation, one obtains a rather uniform sensitivity as to modulationfor a large range of particles.

Each photocell detects a particular brightness which is diminished tosome extent if a foreign particle is in one of the three associatedareas 62' as defined. Brightness as detected by that cell increases ifthe foreign particle is within the area 61 of the projected reticlespoke 61. For a relatively small particle, the output signals of thefour photocells, i.e., with the dirt particle being present in theinstantaneous inspection field, may have a configuration as illustratedin FIG. 5, assuming that the rotation of the dove prism is sufficientlyfast in comparison with the rotation of the wedge prism so that theparticle traverses the viewing areas for all photocells at least once.

FIG. 6 illustrates representatively the output wave of two juxtaposedcells (for example, 51 and 52) in case of a larger dirt patch; theprinciple amplitude excursions occur when the (actual) projection of apatch onto the photocells enters and leaves the area outlined by therespective photocell, with little modulation resulting from the spokes.The principle excursions may even overlap. A clean bottle produces aconstant d-c output of all photocells. It is the unmodulated level ineach of the traces of FIGS. and 6.

A foreign particle which is comparatively small, therefore, produces ineach of these photo detectors, a signal which is an a-c signal,superimposed upon d-c level as monitored by each of the photocells. The

frequency range of the signal is given by Af= N (2 W1: W2). In thisequation the following terms have been used. The value W is therotational speed of the dove prism; as a dove prism produces a rotationof the optical field on its output side at twice its own rotationalspeed, the characteristic rotational sweep speed of the instantaneousfield 45 is 2 w,. The value W2 is the nutational speed, as provided bythe rotation of wedge prism 27. The signs have to be used in theequation because a particle may be close to the center or more to theperiphery of the total inspection field 10a. In the former case, thepassage of an increment of the instantaneous inspection field asprojected onto alternating opaque spokes and windows moves oppositely tothe nutation of the instantaneous inspection field; in the latter casethey move in the same direction. N is a number which defines the ratiobetween the full circle (2 1r and twice the'sector angle of an opaquereticle spoke, or, in case they are equal, the sector angle of an opaquereticle spoke plus the sector angle of a juxtaposed window, as theytogether define a full wavelength of produced (fine) modulation.Therefore, in case of FIG. 2, N=10.

Representatively now let w be 416 and W 143, then A f is defined byupper and lower limit frequencies, respectively of 2,430 to 5,590 cps.Considering the output signal of each photocell individually, forexample, as shown in FIG. 6, each wave train as produced by anyphotocell has additionally a fundamental equal to the rotational speedfrequency of the rotating field due to the coarse modulation provided bythe system. That fundamental frequency is 2 w, 832 cps for the numericalexample, and is, of course, per se, very pronounced in case of FIG. 6.However, this fundamental should not be used directly for the detectionof large particles as the sweep frequencies themselves should beexcluded as noise. Nevertheless, the output train of each photocell,even in case of FIG. 6, still has a strong overall component within thatrange Af of reticle spoke modulation, provided the signals ofneighboring photocells are not algebraically combined. Thus, if theoutput signals of adjacently positioned cells are processed individuallyas to detection of components in the frequency range A f N (2 w, 1 W2),even large patches having produced illumination excursions forindividual photocells as shown separately for two adjacent cells in FIG.6, will produce strong components within that frequency range A f.

As is illustrated schematically in FIG. 2 the photocells not having acommon boundary such as 51 and 53 on one hand, and 52 and 54 on theother hand, are connected in parallel and respectively connected totuned amplifiers 71 and 72. These amplifiers are, for

example, tuned to frequencies within the range N (2 w W2). The detectionand tuning range can have a narrow band if 2 w, w which is beneficialfor noise rejection.

If two diametrically positioned cells are, as illustrated, connected inparallel, then the fundamental frequency in each such individualdetection circuit, due to modulation resulting from sweeping of theinspection field over the individual photocells, is actually 4.w or1,664 cps for the numerical example given. Thus, only a minor extensionof the frequency detection range at the lower end permits utilization ofthat fundamental, resulting particularly strong from large patches. Theupper limit needed for the detection band was given above by N (2 w,W2). Let M be the number of different sector-shaped photocells used.Then the lower limit frequency could be redefined by 2 W X M/2, in caseevery other cell around this circular arrangement of cells connects tothe same circuit and provided w M N (2 W W2) or (2N-M/N) W w which isthe case normally. In the chosen example M 4 so that the lower limitfrequency is 1.664 kc. In general, the detection band can be narrowed byselecting M/2 not too much smaller than N. Most importantly, thisredefined detection band still excludes the sweep frequency 2 W itself,which is beneficial, even necessary, for noise suppression.

The outputs of tuned circuits are respectively fed to threshold devices73 and 74 for reasons of noise suppression. Whenever a detectedoscillation within the tuned range exceeds its threshold value, it ispermitted to be applied to the signal input of a gate 75. This signalcan be regarded as the equivalent of a true or a false signal. It istrue, when a single or several foreign particles have been detected, andfalse when not.

Gate 75 is opened only during the inspection period, i.e., when thebottle container is, in fact, underneath the inspection station 12,which, of course, is only a very short period of time. The output signalof gate 75, whatever the case may be, is provided to the reject controlcircuit 16 which is of no immediate interest as far as the invention isconcerned. Circuit 10 will essentially include a storage device whichresponds to the presence of a reject command signal as provided by theinspection station 12 and stores the signal, if that command is a truesignal, until the container has traveled from the inspection station tothe reject device 15, whereupon the rejection process is triggered.

It is evident, from the discussion in relation to the traces of FIG. 6,that the fine-coarse modulation of the signal as processed in each ofthe two electrical circuit channels is essentially free from theselfcancellation effect resulting from large objects or patches, unlesssuch patches cover essentially the entire or most of the bottle bottom,in which case the d-c signal level has to be processed separately. Thesystem eliminates also another type of cancellation effect. If a foreignparticle is positioned to be covered at any instant by the projectionofa reticle spoke, while a second foreign dirt particle is not socovered by the projection of a reticle spoke, it may occur that afterrotation of the instantaneous field equal to the sector angle of areticle spoke, the relationship is reversed. In this case the twophotocells produce a-c components in opposite phase. The full drawnexcursions in FIG. represent, for example, the first foreign particle,the dotted excursions are produced by the second foreign particle. If,and as long as, these signals were additively combined, they may cancel,orat least weaken, each other so that the composite signal does notexceed the detection threshold. Even if the particles were closetogether, there always will be instants where one particle is in thedetection range of one cell while the other one is in the range ofanother cell. Since neighboring or adjacent cells connect to differentcircuits, there will be at least one excursion in the output of eachcell that is not canceled.

As an operating condition it has been set forth that two adjacentphotocells provide these outputs to different circuits. This does notimply that two nonadjacent photocells have to provide their outputs tothe same circuit; nevertheless the connection is made in that manner,particularly to include the resulting coarse modulation in the signaltrains within the detection band while still excluding the sweepfrequencies of the fields themselves. The situation should thus bediscussed that two foreign particles, for example, have approximatelydiametrical opposite positions, so that there is alternating coverage byspokes on photocells feeding the same detector circuit. However, in viewof the varying position of the center of the progressing instantaneousfield of inspection due to mutation, that relation will not bemaintained for long. Instrumental here is also the selection of a ratherlarge speed differential between nutational and rotational speed of theinstantaneous field of inspection with a relatively high rotationalspeed of the dove prism, and a relatively low nutational speed asprovided by the wedge prism.

One can see from the relation above that the frequency band of interestcan be shifted to a high range if the number of reticle spokes isrelatively large so that nutational and rotational frequenciesthemselves are outside of the detection band. However, with an increasednumber of spokes the probability of cancelation effects with the area ofthe same photocell increases, unless the number of photocells used islikewise increased. Thus, there should be not too many opaque or maskingspokes per photo detector, otherwise the reticle induced modulationmaybe too weak for large particles. Two spokes per photocell asillustrated, were found to be highly suitable to obtain achievingsatisfactory results.

The invention is not limited to the embodiments described above, but allchanges and modifications thereof, not constituting departures from thespirit and scope of the invention are intended to be covered by thefollowing claims.

What is claimed is:

1. In a system for inspecting a container for particles of foreignmatter,

a source of radiant energy disposed relative to the container to providean energized field for inspection; plurality of radiant energy sensitivemeans each constructed to receive radiant energy from the energizedfield and producing a signal at any instant in accordance with theradiant energy received at that instant; first means for defining anindividual instantaneous inspection field for each of said sensitivemeans of the plurality, and within said energized field for inspectionand coupling said individual instantaneous inspection fieldsrespectively to the sensitive means of the plurality, the severalinstantaneous inspection fields as associated with all of the sensitivemeans of the plurality covering less than the energized field forinspection;

second means coupled to the first means to cause the severalinstantaneous inspection fields to rotate about a common center;

third means coupled to the first means to cause that common center torotate so that the several individual fields of inspection sweep theentire energized field for inspection; and

tuned circuit means connected to the radiation sensitive means of theplurality to be responsive to pass band signal components in saidsignals, the passband being defined by the rotational speeds as providedby the second and third means.

2. In a system for inspecting a container for particles of foreignmatter;

a light source disposed relative to the container to provide anilluminated field for inspection;

a plurality of light sensitive means disposed to receive light from theilluminated field, each light sensitive means of the plurality producingan electrical signal at any instant in accordance with the light asreceived at that instant;

light stop means on each of the light sensitive means separating theradiation sensitive area of the light sensitive means into at least twononcontiguous portions;

optical means for directing at any instant and onto each light sensitivemeans of the plurality, light from a particular area of the illuminatedfield, the particular areas from which light is directed to all saidlight sensitive means at any instant defining a common instantaneousinspection field;

means coupled to the optical means for varying the particular area fromwhich a light sensitive means of the plurality receives light in adirection which when projected upon the light sensitive means isessentially transverse to the direction of the predominant extension ofthe light stop means thereon;

means coupled to the optical means for progressively varying the commoninspection field to progressively cover the entire illuminated field;and

tuned circuit means connected to the light sensitive means of theplurality to be responsive to a passband signal component in saidsignal, the passband being defined by the speed for varying as providedby the first and second means.

3. In a system as set forth in claim 2, the circuit means including aplurality of tuned circuits, a circuit of the plurality being connectedto those light sensitive means of the plurality not having a commonboundary.

4. In a system for inspecting a container for particles of foreignmatter, the combination comprising:

means disposed relative to the container for illuminatin g the containerto provide a field of light as a total field of inspection modulated bythe optical characteristics of the container and any particle in thecontainer;

a plurality of light sensitive members disposed in spaced relationshipto each other and to said field of inspection;

optical means for providing to said light sensitive means radiation froman instantaneous field of inspection of said total field of inspection,each light sensitive means of the plurality receiving light from adifferent portion of the instantaneous field of inspection, andincluding means for causing redirecting the light as provided to thesensitive means corresponding to a rotation of the instantaneous fieldabout its center and further corresponding to nutation of theinstantaneous field of inspection about the center of and within saidtotal field of inspection;

reticle means disposed at the light sensitive means to define for eachlight sensitive means at least one blind zone and at least one zonesensitive to the radiation as provided from a portion of theinstantaneous field of inspection by said optical means; and

means connected to said light sensitive means to receive therefromsignals representative of the radiation as received by the lightsensitive means at any instant.

5. In a system for inspecting a container for particles of foreignmatter, the combination comprising:

means disposed relative to the container for illuminating the containerto provide a field of light as a total field of inspection modulated bythe optical characteristics of the container and any particle in thecontainer;

optical means disposed for providing radiation from an instantaneousfield of inspection of said total field of inspection for reception in aparticular plane as a projected inspection field and including means forrotating the projected inspection field about its center and forredirecting the optical means corresponding to nutation of theinstantaneous field of inspection about the center of and within saidtotal field inspection;

a plurality of light sensitive means disposed in a particular pattern inthe particular plane, leaving zones of nonsensitivity between them, eachreceiving radiation from a portion of the instantaneous field ofobservation, the light sensitive means together receiving radiation ofless than the entire instantaneous field of inspection corresponding tosaid nonsensitive zones; and

means connected to said light sensitive means to receive therefromsignals representative of the radiation as received by the lightsensitive means at any instant.

6. In a system as set forth in claim 5, there being a stationary reticlemeans disposed in the plane of the light sensitive means to define aplurality of blind zones and a plurality of transparent zones for thelight sensitive means to'be sensitive at the transparent zones toradiation from the instantaneous field of inspection as provided by theoptical means.

7. In a system for inspecting a container for particles of foreignmatter;

a light source disposed relative to the container to provide anilluminated field for inspection;

a plurality of light sensitive means disposed to Y receive light fromthe illuminated field, each light sensitive means of the pluralityproducing an electrical signal at any instant in accordance with thelight as received at that instant;

optical means for directing, at any instant and onto each lightsensitive means of the plurality, light from a particular area of theilluminated field, the particular areas from which light is directed toall said light sensitive means at any instant defining a commoninstantaneous inspection field; I

first means coupled to the optical means for progressively varying theparticular areas as respectively inspected by each said light sensitivemeans within said common inspection field;

second means coupled to the, optical means for progressively varying thecommon inspection field to progressively cover the entire illuminatedfield; and

tuned circuit means connected to the light sensitive means of theplurality to be responsive to a passband signal component in saidsignal, the passband being defined by the speed for varying as providedby the first and second means, there being light stops provided on thelight sensitive means of the plurality.

8. In a system for inspecting a container for particles of foreignmatter;

a light source disposed relative to the container to provide anilluminated field for inspection;

a plurality of light sensitive means disposed to receive light from theilluminated field, each light sensitive means of the plurality producingan electrical signal at any instant in accordance with the light asreceived at that instant;

optical means for directing, at any instant and onto each lightsensitive means of the plurality, light from a particular area of theilluminated field, the particular areas from which light is directed toall said light sensitive means at any instant defining a commoninstantaneous inspection field;

first means coupled to the optical means for progressively varying theparticular areas as respectively inspected by each said light sensitivemeans within said common inspection field;

second means coupled to the optical means for progressively varying thecommon inspection field to progressively cover the entire illuminatedfield; and

tuned circuit means connected to the light sensitive means of theplurality to be responsive to a passband signal component in saidsignal, the passband being defined by the speed for varying as providedby the first and second means, the circuit means including a pluralityof tuned circuits, each circuit of the plurality being connected tothose light sen sitive means of the plurality not having a commonboundary.

9. In a system for inspecting a container for small particles of foreignmatter, a source of light disposed relative to the container forproviding light to the container to provide an illuminated field forinspection;

first means including a rotatable prism disposed relative to thecontainer for continuously receiving light from a portion of theilluminated field of the container;

second means operatively coupled to the first means for obtainingrotation of the prism to progressively vary the area from which light isreceived from within the illuminated field;

a second rotatable prism disposed in the path of the light as receivedby the first prism for defining an eccentric inspection field withinsaid illuminated field;

means coupled to the second prism for providing rotation to the secondprism for rotating the eccentric field of inspection about the axis ofrotation of the second prism;

a plurality of light sensitive means disposed to receive the light fromthe light path after passage through the first and second prisms andfrom within the eccentric inspection field; and

circuit means coupled to said light sensitive means for being responsiveto particular bandpass signals representative of foreign particles inthe container, there being light stops provided on the light sensitivemeans of the plurality.

10. In a system for inspecting a container for small particles offoreign matter, a source of light disposed relative to the container forproviding light to the container to provide an illuminated field forinspection;

first means including a rotatable prism disposed relative to thecontainer for continuously receiving light from a portion of theilluminated field of the container;

second means operatively coupled to the first means for obtainingrotation of the prism to progressively vary the area from which light isreceived from within the illuminated field;

a second rotatable prism disposed in the path of the light as receivedby the first prism for defining an eccentric inspection field withinsaid illuminated field;

means coupled to the second prism for providing rotation to the secondprism for rotating the eccentric field of inspection about the axis ofrotation of the second prism;

a plurality of light sensitive means disposed to receive the light fromthe light path after passage through the first and second prisms andfrom within the eccentric inspection field; and

circuit means coupled to said light sensitive means I for beingresponsive to particular bandpass signals representative of foreignparticles in the container, the circuit means including a plurality oftuned circuits, each circuit of the plurality being connected to thoselight sensitive means of the plurality not having a common boundary.

11'. In a system for inspecting a container for particles of foreignmatter:

a source of radiant energy disposed relative to the container to providean energized field through the container;

first means disposed relative to the energized field for defining aninstantaneous field for inspection where the instantaneous fieldconstitutes a portion of the energized field;

second means operatively coupled to the first means for obtaining arotation of the instantaneous field about the energized field at a firstparticular frequency;

a plurality of third means disposed relative to the second means forsensing the energy in selected portions of the energized field;

fourth means disposed relative to the energized field for rotating theinstantaneous field past the plurality of third means at a secondparticular frequency greater than the first particular frequency; and

fifth means operatively coupled to the plurality of third means in aparticular relationship for receiving signals in a particular frequencyrange related to the first and second particular frequencies to providean indication of large and small particles in the container, the fifthmeans being connected to pairs of non-adjacent third means to providethe indication of large and small particles in the container.

12. In a system for inspecting a container for particles of foreignmatter:

means for directing energy through the container in a particular area todefine an energized field;

first means disposed relative to the energized field for progressivelyinspecting particular portions of the energized field on a cyclic basisat a particular rate;

a plurality of energy-responsive means disposed in spaced relationshipto one another to receive the energy from the particular portions of theenergized field;

second means disposed between the first means and the plurality ofenergy-responsive means for scanning the energy in the particularportions of the energy-responsive means at a second rate greater thanthe first rate; and

third means connected to the energy-responsive means in the plurality ina particular relationship to produce output signals having alternatingcomponents representing small and large particles in the container, thefirst and second means being optical and being rotatable at frequenciesrelated to the first and second rates and the third means beingresponsive only to signals having frequency components in a frequencyrange dependent upon the arithmetical sum and the arithmeticaldifference of the first and second rates to produce the output signalshaving alternating components representing the small and large particlesin the container, the third means being connected to non-adjacent pairsof the energy-responsive means.

1. In a system for inspecting a container for particles of foreignmatter, a source of radiant energy disposed relative to the container toprovide an energized field for inspection; a plurality of radiant energysensitive means each constructed to receive radiant energy from theenergized field and producing a signal at any instant in accordance withthe radiant energy received at that instant; first means for defining anindividual instantaneous inspection field for each of said sensitivemeans of the plurality, and within said energized field for inspectionand coupling said individual instantaneous inspection fieldsrespectively to the sensitive means of the plurality, the severalinstantaneous inspection fields as associated with all of the sensitivemeans of the plurality covering less than the energized field forinspection; second means coupled to the first means to cause the severalinstantaneous inspection fields to rotate about a common center; thirdmeans coupled to the first means to cause that common center to rotateso that the several individual fields of inspection sweep the entireenergized field for inspection; and tuned circuit means connected to theradiation sensitive means of the plurality to be responsive to pass bandsignal components in said signals, tHe passband being defined by therotational speeds as provided by the second and third means.
 2. In asystem for inspecting a container for particles of foreign matter; alight source disposed relative to the container to provide anilluminated field for inspection; a plurality of light sensitive meansdisposed to receive light from the illuminated field, each lightsensitive means of the plurality producing an electrical signal at anyinstant in accordance with the light as received at that instant; lightstop means on each of the light sensitive means separating the radiationsensitive area of the light sensitive means into at least twononcontiguous portions; optical means for directing at any instant andonto each light sensitive means of the plurality, light from aparticular area of the illuminated field, the particular areas fromwhich light is directed to all said light sensitive means at any instantdefining a common instantaneous inspection field; means coupled to theoptical means for varying the particular area from which a lightsensitive means of the plurality receives light in a direction whichwhen projected upon the light sensitive means is essentially transverseto the direction of the predominant extension of the light stop meansthereon; means coupled to the optical means for progressively varyingthe common inspection field to progressively cover the entireilluminated field; and tuned circuit means connected to the lightsensitive means of the plurality to be responsive to a passband signalcomponent in said signal, the passband being defined by the speed forvarying as provided by the first and second means.
 3. In a system as setforth in claim 2, the circuit means including a plurality of tunedcircuits, a circuit of the plurality being connected to those lightsensitive means of the plurality not having a common boundary.
 4. In asystem for inspecting a container for particles of foreign matter, thecombination comprising: means disposed relative to the container forilluminating the container to provide a field of light as a total fieldof inspection modulated by the optical characteristics of the containerand any particle in the container; a plurality of light sensitivemembers disposed in spaced relationship to each other and to said fieldof inspection; optical means for providing to said light sensitive meansradiation from an instantaneous field of inspection of said total fieldof inspection, each light sensitive means of the plurality receivinglight from a different portion of the instantaneous field of inspection,and including means for causing redirecting the light as provided to thesensitive means corresponding to a rotation of the instantaneous fieldabout its center and further corresponding to nutation of theinstantaneous field of inspection about the center of and within saidtotal field of inspection; reticle means disposed at the light sensitivemeans to define for each light sensitive means at least one blind zoneand at least one zone sensitive to the radiation as provided from aportion of the instantaneous field of inspection by said optical means;and means connected to said light sensitive means to receive therefromsignals representative of the radiation as received by the lightsensitive means at any instant.
 5. In a system for inspecting acontainer for particles of foreign matter, the combination comprising:means disposed relative to the container for illuminating the containerto provide a field of light as a total field of inspection modulated bythe optical characteristics of the container and any particle in thecontainer; optical means disposed for providing radiation from aninstantaneous field of inspection of said total field of inspection forreception in a particular plane as a projected inspection field andincluding means for rotating the projected inspection field about itscenter and for redirecting the optical means corresponding to nutationof the instantaneous field of inspection about the center of and withinsaid total field inspection; a plurality of light sensitive meansdisposed in a particular pattern in the particular plane, leaving zonesof nonsensitivity between them, each receiving radiation from a portionof the instantaneous field of observation, the light sensitive meanstogether receiving radiation of less than the entire instantaneous fieldof inspection corresponding to said nonsensitive zones; and meansconnected to said light sensitive means to receive therefrom signalsrepresentative of the radiation as received by the light sensitive meansat any instant.
 6. In a system as set forth in claim 5, there being astationary reticle means disposed in the plane of the light sensitivemeans to define a plurality of blind zones and a plurality oftransparent zones for the light sensitive means to be sensitive at thetransparent zones to radiation from the instantaneous field ofinspection as provided by the optical means.
 7. In a system forinspecting a container for particles of foreign matter; a light sourcedisposed relative to the container to provide an illuminated field forinspection; a plurality of light sensitive means disposed to receivelight from the illuminated field, each light sensitive means of theplurality producing an electrical signal at any instant in accordancewith the light as received at that instant; optical means for directing,at any instant and onto each light sensitive means of the plurality,light from a particular area of the illuminated field, the particularareas from which light is directed to all said light sensitive means atany instant defining a common instantaneous inspection field; firstmeans coupled to the optical means for progressively varying theparticular areas as respectively inspected by each said light sensitivemeans within said common inspection field; second means coupled to theoptical means for progressively varying the common inspection field toprogressively cover the entire illuminated field; and tuned circuitmeans connected to the light sensitive means of the plurality to beresponsive to a passband signal component in said signal, the passbandbeing defined by the speed for varying as provided by the first andsecond means, there being light stops provided on the light sensitivemeans of the plurality.
 8. In a system for inspecting a container forparticles of foreign matter; a light source disposed relative to thecontainer to provide an illuminated field for inspection; a plurality oflight sensitive means disposed to receive light from the illuminatedfield, each light sensitive means of the plurality producing anelectrical signal at any instant in accordance with the light asreceived at that instant; optical means for directing, at any instantand onto each light sensitive means of the plurality, light from aparticular area of the illuminated field, the particular areas fromwhich light is directed to all said light sensitive means at any instantdefining a common instantaneous inspection field; first means coupled tothe optical means for progressively varying the particular areas asrespectively inspected by each said light sensitive means within saidcommon inspection field; second means coupled to the optical means forprogressively varying the common inspection field to progressively coverthe entire illuminated field; and tuned circuit means connected to thelight sensitive means of the plurality to be responsive to a passbandsignal component in said signal, the passband being defined by the speedfor varying as provided by the first and second means, the circuit meansincluding a plurality of tuned circuits, each circuit of the pluralitybeing connected to those light sensitive means of the plurality nothaving a common boundary.
 9. In a system for inspecting a container forsmall particles of foreign maTter, a source of light disposed relativeto the container for providing light to the container to provide anilluminated field for inspection; first means including a rotatableprism disposed relative to the container for continuously receivinglight from a portion of the illuminated field of the container; secondmeans operatively coupled to the first means for obtaining rotation ofthe prism to progressively vary the area from which light is receivedfrom within the illuminated field; a second rotatable prism disposed inthe path of the light as received by the first prism for defining aneccentric inspection field within said illuminated field; means coupledto the second prism for providing rotation to the second prism forrotating the eccentric field of inspection about the axis of rotation ofthe second prism; a plurality of light sensitive means disposed toreceive the light from the light path after passage through the firstand second prisms and from within the eccentric inspection field; andcircuit means coupled to said light sensitive means for being responsiveto particular bandpass signals representative of foreign particles inthe container, there being light stops provided on the light sensitivemeans of the plurality.
 10. In a system for inspecting a container forsmall particles of foreign matter, a source of light disposed relativeto the container for providing light to the container to provide anilluminated field for inspection; first means including a rotatableprism disposed relative to the container for continuously receivinglight from a portion of the illuminated field of the container; secondmeans operatively coupled to the first means for obtaining rotation ofthe prism to progressively vary the area from which light is receivedfrom within the illuminated field; a second rotatable prism disposed inthe path of the light as received by the first prism for defining aneccentric inspection field within said illuminated field; means coupledto the second prism for providing rotation to the second prism forrotating the eccentric field of inspection about the axis of rotation ofthe second prism; a plurality of light sensitive means disposed toreceive the light from the light path after passage through the firstand second prisms and from within the eccentric inspection field; andcircuit means coupled to said light sensitive means for being responsiveto particular bandpass signals representative of foreign particles inthe container, the circuit means including a plurality of tunedcircuits, each circuit of the plurality being connected to those lightsensitive means of the plurality not having a common boundary.
 11. In asystem for inspecting a container for particles of foreign matter: asource of radiant energy disposed relative to the container to providean energized field through the container; first means disposed relativeto the energized field for defining an instantaneous field forinspection where the instantaneous field constitutes a portion of theenergized field; second means operatively coupled to the first means forobtaining a rotation of the instantaneous field about the energizedfield at a first particular frequency; a plurality of third meansdisposed relative to the second means for sensing the energy in selectedportions of the energized field; fourth means disposed relative to theenergized field for rotating the instantaneous field past the pluralityof third means at a second particular frequency greater than the firstparticular frequency; and fifth means operatively coupled to theplurality of third means in a particular relationship for receivingsignals in a particular frequency range related to the first and secondparticular frequencies to provide an indication of large and smallparticles in the container, the fifth means being connected to pairs ofnon-adjacent third means to provide the indication of large and smallParticles in the container.
 12. In a system for inspecting a containerfor particles of foreign matter: means for directing energy through thecontainer in a particular area to define an energized field; first meansdisposed relative to the energized field for progressively inspectingparticular portions of the energized field on a cyclic basis at aparticular rate; a plurality of energy-responsive means disposed inspaced relationship to one another to receive the energy from theparticular portions of the energized field; second means disposedbetween the first means and the plurality of energy-responsive means forscanning the energy in the particular portions of the energy-responsivemeans at a second rate greater than the first rate; and third meansconnected to the energy-responsive means in the plurality in aparticular relationship to produce output signals having alternatingcomponents representing small and large particles in the container, thefirst and second means being optical and being rotatable at frequenciesrelated to the first and second rates and the third means beingresponsive only to signals having frequency components in a frequencyrange dependent upon the arithmetical sum and the arithmeticaldifference of the first and second rates to produce the output signalshaving alternating components representing the small and large particlesin the container, the third means being connected to non-adjacent pairsof the energy-responsive means.